Magnetic separation apparatus and treating methods involving magnetic separation



Feb. 28, 1961 M. J. GREAVES 2 7 96 MAGNETIC SEPARATION APPARATUS ANDTREATING METHODS INVOLVING MAGNETIC SEPARATION Filed April 18, 1958 3Sheets-Sheet 1 TOE INVENTOR MELVIN J- GREAVES ATTORNEYS \PN GM 1+=ltliiiL lll inv-i 1 x I ll Y on a B Feb. 28, 1961 M. J. GREAVES I2,973,096

MAGNETIC SEPARATION APPARATUS AND TREATING METHODS INVOLVING MAGNETICSEPARATION Filed April 18, 1958 a Sheets-Sheet 2 FIG. 2

INVENTOR. MELVIN J.G R [AVE 5 ATTORNEYS Feb. 28, 1961 M. J. GREAVES2,973,

MAGNETIC SEPARATION APPARATUS AND TREATING METHODS mvonvmc MAGNETICSEPARATION "Filed April 18, 1958 s Sheets-Sheet 3 FIG 6 INVENTOR. MELVINJ. GREAVE AITORNEYS United States Melvin J. Greaves, Parma, Ohio,assignor to Robert A. Cummings, Jr., Pittsburgh, Pa.

Filed Apr. 18, 1958, Ser. No. 729,411

7 Claims. (Cl. 210-65) This application relates to magnetic separationapparatus and treating methods involving magnetic separation. Broadlythe invention relates to the separation of materials having differentmagnetic susceptibilities entrained in a fluid flowing in a movingmagnetic field. Specifically the invention has utility in flotationseparation, conveying and like processes and apparatus in which magneticmaterial, generally finely divided, is employed to increase the buoyancyor apparent specific gravity of a liquid medium which is used for thetreatment or conveying of bulk material.

In the specification and drawing the invention is illustrated inconnection with cleaning of coal by the flotation process, but it willbe understood that the invention has other possible and equallyimportant applications.

Coal, as mined, has mixed with it slate and other foreign matters whichare referred to generally as gangue which is separated from the coalbefore marketing. In the flotation process of cleaning coal, the coal,as mined, is discharged into a suitable receptacle containing theflotation treating liquid upon which the coal floats, the heaviermaterials comprising the gangue sinking to the bottom. The coal, free ofgangue, is then removed from the surface of the flotation liquid.

The flotation liquid, for the intended purpose, has a specific gravitygreater than that of the coal and a less specific gravity than thoseportions of the material to be separated from the coal, whereby the coalwill float on the liquid and the materials to be separated will sink inthe liquid. The flotation liquid is water having entrained thereinfinely divided solid materials which are insoluble in water and whosespecific gravity is high enough so that the resultant mixture has thedesired specific gravity for the purpose. Heretofore the procedure wasto introduce into the water finely divided magnetic material such asmagnetite or ferrosilicon and after use to magnetically separate themagnetic material from the water and return it for re-use. It has beenfound, however, that during such magnetic separation the materialflocculated, thereby rendering it unfit for further re-use, until thematerial had been deflocculated.

In the present invention, one of the advantages is that the magneticmaterial is not flocculated during separation and, therefore, may beimmediately returned for re-use without further treatment. In thepresent method of recovering the substantially magnetic material fromthe liquid comprises flowing the liquid in a stream or through a conduitand impelling toward one side of the stream or conduit the magneticmaterial by a moving magnetic field and then separately collecting themagnetic material and the substantially magnetic material free liquid. Ifound it desirable that the magnetic field move parallel to thedirection of flow of the liquid and that the speed of movement of themagnetic field approximate the speed of flow of at least that portion ofthe liquid containing the magnetic material. Preferably, a polyphasealternating magnet located alongside the conduit provides the magneticfield. Such a magnet has the characteristic atent O i 2,973,096 PatentedFeb. 28, 1961 that the magnetic field moves along the conduit. Themagnet is designed and wound so that the magnetic field advances alongthe conduit in the same direction as the flow of the liquid within theconduit and at the desired speed. The magnetic material is thus impelledby the magnet, preferably being attracted toward it, which promotes thedesired separation.

With such a magnet the magnetic material not becoming permanentlymagnetized the parties have no attraction one to the other and thuspreventing flocculation.

For the purposes of illustration the magnetic material containing liquidis flowed generally horizontal so that the magnetic material within theliquid is drawn downwardly within the liquid by a magnetic field whichis moving in the direction of flow. Thus substantially magnetic materialfree liquid is delivered from above the downwardly drawn magneticmaterial.

It has been found that all of the material within the conduit, when sotreated, will not move at the same velocity. One cause of this is thatthe magnetic material being drawn toward one side of the direction offlow tends by reason of the increased viscosity of that portion of theliquid to be slower than at the opposite side. The maximum velocity ofthe stream flowing within the conduit is therefore near the geometriccenter thereof with the minimum velocity adjacent the side of theconduit nearest the magnet. It is desirable, therefore, that themagnetic field of the magnet moving along the side of the conduit at aspeed approximately equal to the speed of flow of the contents of theconduit which contains the magnetic material. Optimum efliciency isobtained by this method.

The intensity of the magnetic field created by any magnet decreasesrapidly as the air gap distance from the face of the pole of the magnetincreases, There is an economic limit to the magnetic field intensity atthe base of the. pole due to the change in the magnetic properties ofthe iron ore under high magnetic flux densities, to the problem ofcooling the magnet and to leakage of flux which does not pass throughthe face of the poles. These factors make it desirable to restrict thedistance from the magnet to the fartherest removed magnetic .material atthe zone of entry into the magnetic field.

Once the magnetic material is in sufficiently intense magnetic field toprevent it leavingthe proximity of the magnet, the dimension of theconduit parallel to the direction of the magnetic attraction may beincreased without appreciably affecting the operation of the unit.

It is desirable, therefore, to confine the dimension of the streamparallel to the direction of magnetic attraction to a minimum in thezone of entry of the stream into the magnetic field and increase thatdimension in a zone advanced in the direction of flow relatively to thefirst mentioned zone. Preferably the cross-sectional area of the streamis designed so that the velocity of flow of the portion of the streamcontaining the magnetic material is substantially equal to the speedofmovement of the magnetic field along the conduit. To this end I maypre-determinedly increase in the direction of flow the dimensionof. thestream which is parallel to thedirection of magnetic attraction anddecrease in the direction of flow the dimension of the stream normal tothe dimension which is parallel to the direction of magnetic attraction.To reduce energy losses at the point where the stream divides near theend of the magnetic field, it is desirable to employ a relatively largedimension of the stream parallel to the direction of magnetic attractionat that point. Afurther advantage of increasing the dimension of thestream parallel to the direction of magnetic attraction at thedivisionpoint is that a better separation of magnetic material and magneticmaterialfree liquid is effected.

For most effective separation the concentration of magnetic material inthe liquid may be controlled by recirculating a portion of either thecomponent containing the magnetic material or the magnetic material freecomponent of the liquid. It is desirable that the' magnetic materialalong the side of the conduit adjacent the magnet form a low resistantcircuit for the magnetic flux and the concentration of magnetic materialin the liquid is controlled with this end in view. The less magneticmaterial in the liquid before the greater is the resistance in themagnetic circuit due to the small dimension of the portion of the streamoccupied by the magnetic material. The more magnetic material in theliquid the greater is the tendency for the conduit to clog and the moreof the magnetic material is admixed with the desirably magnetic materialfree liquid.

I provide an improvement in the treatment of bulk material in which thebulk material is admixed with liquid and finely divided magneticmaterial and subsequently separated therefrom, which comprises the stepsof magnetically separating a portion of the liquid from the finelydivided magnetic material contained therein while maintaining finelydivided magnetic material in deflocculated state and returning thedeflocculated finely divided magnetic material for re-use. Analternating current magnetic field effects the desired separationwithout causing flocculation of the magnetic material. The separatedliquid may be returned for re-use and may be filtered en route. Theseparated liquid may be employed for washing the bulk material. In apreferred treatment Fig. 6 is a fragmentary cross-section view toenlarged scale taken in the plane VIVI of Fig. 5.

Referring now more particularly to Figure 1, there is shown a fragmentof a reservoir designated generally by reference numeral 2 and which hasa sloping bottom as shown. In the portion of the reservoir which appearsin Fig. 1 is a flotation liquid 3 on which floats coal 4. The reservoir2 may be the tank of coal washer or it may be the delivery terminus of apipe line through which coal has been delivered in the flotation liquidas a carrier. in either event the flotation liquid 3 consists of waterand finely divided magnetic material; I prefer to employ magnetite asthe finely divided magnetic mapasses about a sprocket 6 which turns inthe clockwise I lift the bulk material out the admixed liquid and finelydivided magnetic material withdraw a portion of the admixed liquid andfinely divided magnetic material, magnetically separate the withdrawnliquid from the finely divided magnetic material contained therein whilemaintaining the finely divided magnetic material in deflocculated state,return the deflocoulated finely divided magnetic material for re-use,employ the thus separated liquid for washing the bulk material which hasbeen lifted out of the admixed liquid and finely divided magneticmaterial and conduct the washing liquid back into the admixed liquid andfinely divided magnetic material.

{I also provide, in a flotation or like process in which finely dividedmagnetic material is employed to increase the buoyancy of a liquidtreating medium, the steps of separating a portion of the liquid from afinely divided magnetic material contained therein by an alternatingcurrent magnetic field and returning the thus separated finely dividedmagnetic material for re-use. This separation is preferably effectedmagnetically while maintaining the finely divided magnetic material indeflocculated state as above described.

I further provide apparatus for carrying out in improved manner thenovel methods above referred to and which will be more fully describedbelow.

In the accompanying drawings I have shown certain present preferredembodiments of the invention and have illustrated certain presentpreferred methods of practicing the same, in which:

Fig. 1 is a diagram generally in the form of a vertical cross-sectionillustrating a coal flotation process and apparatus;

Fig. 2 is a plan view to enlarged scale of the separating conduit of theapparatus illustrated in Fig. 1 with the coil assembly shown inconnection therewith;

Fig. 3 is a vertical cross-sectional elevation through the conduit shownin Fig. 2 with the coil assembly shown in section adjacent to the coilsupporting core.

Fig. 3a is a view of the circuit diagram illustrating current flowthrough the magnets of Figs. 2 and 3;

Fig. 4 is a more or less diagrammatic fragmentary view of another formof separator;

Fig. 5 is a similar view of still another form of separator; and

direction viewing Fig. 1 when the apparatus is in use. As the conveyoroperates it lifts the coal out of the liquid and delivers it to atransverse belt conveyor shown in cross-section at 7. If the reservoir 2is a coal washer tank the opposite portions of the tank (i.e., thatportion not shown in Fig. 1) has an inclined bottom like the portionshown but inclined in the opposite direction and the endless conveyor 5extends from the bottom of the tank to a portion above the tank wall ateach end. The flights of the flight conveyor may be employed to push thegangue and other matter to be separated from the coal upwardly along theopposite inclined bottom portion of the tank to discharge the same fromthe tank, one conveyor thus serving to deliver the coal at one side ofthe tank and the gangue at the opposite side. Such an arrangement isconventional and does not constit-ute my invention.

1 provide a conduit or separator for separating water from magnetite.The conduit is designated 8 and is shown to large scale in Figs. 2 and3. Beneath the conduit 8 is a polyphase alternating current magnet 9(Fig. l) which is disposed close to the under surface of the conduit 8and which operates in known manner to produce by alternating current amagnetic field tending to draw downwardly the particles of magnetite,the magnetic field at the same time moving toward the right, viewingFig. 1. Those skilled in the electrical art know that by proper Windingand proportioning of the magnet coils provision can be made for creatinga magnetic field of desired strength and for movement of that field inthe desired direction at a predetermined speed. Accordingly, onerepresentative circuit arrangement is shown in the diagram illustratedin Fig. 3a. Therein, lines x, y and z are connected to a source ofthree-phase alternating current, not shown. Proper connections forfifteen similar coils a through 0 are illustrated and are such that atraveling magnetic field is produced. The core p consisting of laminatedtransformer iron has eighteen slots which are filled with coils q exceptfor the top half of the first three slots and the bottom half of thelast three slots. This feature is simply one of convenience in order tostandardize on one coil design.

The windings, best illustrated in Fig. 3a, are so dis posed that eachphase produces the resultant magnetic field which occupies a positionelectrical degrees apart from each of the other phases, and since thesewindings are connected to a three-phase circuit, the currents in each ofthem differ by 120 degrees in phase relation from the current in each ofthe others. These two conditions result in the production of a magneticfield of uniform strength which moves at a uniform speed.

A duct 10 leads from the reservoir 2 at 11 to the entrance. end 12 ofthe conduit 8. A pump 13 is positioned in the duct for pumping flotationliquid from the reservoir 2 into the conduit 8. The cross-sectional areaof the conduit 8 is preferably designed so that liquid moves through theconduit in such manner that the portion of the liquid containing themagnetic material advances at approximately the speed of advance of themagnetic field.

The dimension of the conduit 8 parallel to the direction of magneticattraction, i.e., the vertical dimension of the conduit in theembodiment shown in Fig. l, is confined to a minimum in the zone ofentry of the stream into the magnetic field. This zone is the zoneadjacent the entrance end of the conduit. At the entrance end theconduit is relatively wide in the horizontal direction as shown at 14 inFig. 2. The purpose of confining the vertical dimension to a minimum inthe zone of entry of the stream of liquid into the magnetic field is tocause all of the liquid to pass as near as possible to the magnet 9 forthe reason explained above. The vertical dimension of the conduit 8gradually increases from left to right and the horizontal dimensiondecreases as shown in Figs. 2 and 3, the cross-sectional area of theconduit being designed so that the portion of the liquid containing themagnetic material advances at approximately the speed of advance of themagnetic field. The magnet 9 creates a magnetic field which advancesfrom left to right at a velocity determined by the design of the magnet.The magnetic field attracts the particles of magnetite, causing them tomove to the side of the conduit 8 which is against the magnet, i.e., thelower side, viewing Fig. 1. As the liquid advances through the conduitthe magnetite is thus caused to hug the bottom of the conduit whilesubstantially magnetitefree liquid or water moves along the upper partof the conduit. Most effective results are obtained when the velocity ofadvance of the magnetic field is substantially equal to the velocity offlow of that portion of the contents of the conduit 8 containing themagnetite, i.e., the lower portion thereof, viewing Figs. 1 and 3. Theupper portion of the contents of the conduit which is substantiallymagnetite-free water moves somewhat faster than the relatively viscouslower part.

The magnetite is not permanently magnetized or flocculated by theoperation just described. The alternating current field does notpermanently magnetize the particles and in addition their orientation iscontinually being interrupted as they tumble over one another and turnwithin the liquid as they pass through the conduit 8. There is noflocculation of the magnetite, which is delivered from the conduit 8 inthe same unfiocculated condition as upon entry into the conduit 8.

The conduit 8 has at its delivery end two delivery branches, an upperdelivery branch 16 for the substantially magnetite free water and alower delivery branch 17 for the magnetite and enough water to make itflowable (for example, the magnetite and water in the delivery branch 17may be in approximately equal proportions by weight). The upper deliverybranch 16 extends upwardly at an angle of about 45 to the axis of themain portion of the conduit 8 and the lower delivery branch 17 extendsdownwardly at a like angle. At the junction of the main portion of theconduit 8 with the delivery portions 16 and 17 is a divider 18 whichprojects into the main portion of the conduit 8 to separate the contentsof that conduit, causing part of the contents to pass upwardly throughthe delivery portion 16 and part of the contents to pass downwardlythrough the delivery portion 17. The divider 18 is positioned to roughlydivide the magnetite which is disposed at the bottom of the conduit fromthe magnetite-free liquid or water which is disposed at the top of theconduit. Of course there cannot be a perfect separation between themagnetite and the water but the separation is remarkably efiicient andvery little magnetite will pass upwardly through the delivery portion16. Some water will pass downwardly through the delivery portion 17along with the magnetite but the amount of such water will not be great.

The water passing through the delivery portion 16 flows through aconduit 19 to a T 20 where it may flow to the right, viewing Fig. 1,past a valve 21 through a filter 22 and by way of pipe 23 back into thereservoir 2. The water may pass from the T past a valve 24 and through apipe 25 to a spray head 26 where it may be employed for spraying thecoal which has been lifted out of the liquid in the reservoir 2 toremove any adhering magnetite. As the coal rises above the surface ofthe liquid in the reservoir it is covered with magnetite containingliquid which it is desirable to wash off. The liquid sprayed onto thecoal through the spray head 26 is substantially clean water virtuallyfree of magnetite and effectively washes the coal, rendering it veryclean as it is delivered to the cross conveyor 7.

When the spray head 26 is to be used the valve 21 is closed and thevalve 24 is opened so that the water returns 'to the reservoir 2 throughthe spray head. When it is desired to filter the water instead of sprayit onto the coal the valve 21 is opened and the valve 24 is closed andthe water passes through the filter 22 and the pipe 23 back to thereservoir 2.

The magnetite delivered through the delivery portion 17 passes through apipe '27 and past a valve 28 back to the reservoir 2. It is maintainedthroughout the process in deflocculated condition.

For re-circulating a portion of the separated component containingmagnetic material for the purpose of increasing the concentration ofmagnetic material in the liquid entering the conduit 8 I provide aby-pass 29 extending from the pipe 27 to the duct 10 at the intake sideof the pump 13. The by-pass 29 contains a valve 36 which may be openedto a desired extent to control the amount of the component containingmagnetic material, which is re-circulated. The greater the amount or"that component which is re-circulated the greater will be theconcentration of magnetic material in the liquid entering the conduit 8.

For re-circulating a portion of the separated component consisting ofsubstantially magnetic material free liquid for the purpose ofdecreasing the concentration of magnetic material in the liquid enteringthe conduit 8 I provide a by-pass 31 extending from the delivery portion16 to the duct 10 at the intake side of the pump 13. The by-pass 31contains a valve 32 which may be opened to a desired extent to controlthe amount of substantially magnetic material free liquid which isre-circulated. The greater the amount of that component which isrecirculated the less will be the concentration of magnetic material inthe liquid entering the conduit 8.

Thus by proper setting of the valves 30 and 32 one or the other of theseparated components may be re-circulated and through thatre-circulation the concentration of magnetic material in the liquidentering the conduit 8 may be controlled for most efficient separationas explained above.

The structure of Figs. 1, 2 and 3 involves a linear arrangement of themagnet and separating conduit. However the separation can be effectedotherwise. For example, I may employ a circular magnet similar to therotor used in a conventional polyphase wound rotor induction motor and aseparating conduit extending about a portion of the periphery of themagnet. Such a construction has the advantage of freedom from theundesirable end efiects of a linear magnet and has the further advantagethat centrifugal force acts on any particles of relatively nonmagneticmaterial in the arcuate separation conduit causing the relativelynonmagnetic material to follow the outside of the conduit while themagnetic material follows the inside of the conduit. The relativelynonmagnetic material will pass oif with the substantially magneticmaterial free fluid. Such a device would be highly useful in thebeneficiation of iron ore.

In Fig. 4 there is shown diagrammatically an apparatus which may beemployed for the beneficiation of iron ore or in general for theseparation of magnetic and nonmagnetic particles contained in a fluid.There is shown at 33 a circular magnet similar tothe rotor used in aconventional polyphase wound rotor induction motor which, as is known tothose skilled in the art, creates a magnetic field which advancesperipherally about the magnet, the magnet being considered as beingstationarily mounted. The magnet is designed and constructed so that themagnetic field advances in a clockwise direction peripherally of themagnet viewing Fig. 4. The speed of advance of the magnetic field isdetermined by the design of the magnet.

Disposed about a portion of the magnet 33 is a separating conduit 34through which fluid containing magnetic material and also possiblycontaining relatively nonmagnetic material is adapted to flow in theclockwise direction as indicated by the arrows in Fig. 4. The conduit isof minimum dimension radially of the magnet at the entering end and theradial dimension gradually increases from the entering end toward thedischarge end. The transverse dimension of the conduit at right anglesto the radial dimension is designed so that the crosssection of theconduit will be such that the magnetic material will tend to flowthrough the conduit at about the same speed as the speed of advance ofthe magnetic field thcrealong. The conduit 34 is at the discharge enddivided into two discharge branches 35 and 36.

To illustrate the use of the apparatus of Fig. 4 for the separation ofmagnetic and nonmagnetic material carried by a fluid, the fluidcontaining the admixed magnetic and nonmagnetic material flows throughthe entering end of theconduit at 37 until the magnetic field created bythe magnet 33 causes the magnetic particles to move radially inwardly tolie against the inside of the conduit as indicatedat 38. The nonmagneticparticles are not attracted by the magnet but tend to move toward theoutside of the conduit due to centrifugal force as they pass along thecurved conduit The nonmagnetic particles are designated 39. Thus througha combination of the magnetic effect upon the magnetic particles and theeffect of centrifugal force on the nonmagnetic particles those particlesare caused respectively to hug the inner and outer walls of theseparating conduit 34. Thus the magnetic particles pass through thedischarge branch 36 while the nonmagnetic particles pass through thedischarge branch 35. Both the magnetic particles and the nonmagneticparticles are accompanied by a portion of the fluid. If it is desiredthat less fluid pass through one or the other of the discharge branches35 and 36 the crosssectional areas of those branches may be proportionedaccordingly or valves may be provided for adjustably reducing thecross-sectional areas of the discharge branches.

In Figs. and 6 there is shown diagrammatically an apparatus forrecovering substantially magnetic material free liquid from liquidcontaining magnetic material and which comprises a hollow cylindricalpolyphase alternating current magnet 40 similar to the stator of aconventional induction motor creating a magnetic field which advances ina circular path. A separating conduit 41 is disposed within the magnet40, the liquid containing magnetic material being introduced through aduct 42 extending parallel to the axis of the core whence it passesthrough the body of the separating conduit 41, and the separatedmagnetic material and substantially magnetic material and substantiallymagnetic material free liquid are delivered through delivery conduits 43and 44, respectively, which conduits extend parallel to the axis of themagnet. The proportioning of the separating conduit 41 may be the sameas the proportioning of the separating conduits 8 and 34. The magneticmaterial and the substantially magnetic material free liquid areseparated by a divider'45. The magnetic material 46 is drawn outwardlyagainst the outer wall of the separating conduit 41. The centrifugalaction as the liquid passes through the curved conduit 41 cooperateswith the magnetic action in causing the magnetic particles to movedownwardly against the outer wall of the conduit.

The tendency of the portion of the liquid containing magnetic materialas the liquid passes through the separating conduit (and this is trueWhether the separating conduit be straight or curved) is to move withdecreasing velocity'due to its gradually increasing concentration as theseparating is effected. To cause the portion of the liquid containingthe magnetic material in the separating conduit to move at substantiallyconstant velocity so that'that portion of the contents of the separatingconduit may move at a velocity which is substantially equal to thevelocity of movement of the magnetic field the cross-section of theseparating conduit will normally be reduced from a relatively greatcross-section at the. entrance end of the separating conduit to arelatively small cross-section at the discharge end of the separatingconduit. For example, in one construction the cross-sectional area ofthe separating conduit at the entrance end is almost double thecross-sectional area of the separating conduit at the discharge end. Theresult of this is, of course, to cause increase in the speed of flowthrough the separating conduit of the liquid as a whole but the effectof the decrease in cross-section simply counteracts the tendency of theportion of the liquid containing the magnetic material to slow up due toits increased concentration, the net result being that the portion ofthe liquid containing the magnetic material moves at approximatelyuniform velocity. The exact design of the separating conduit dependsupon the particular conditions of operation including the material beingtreated. Generally speaking, however, when the magnetic field advancesat uniform velocity as would normally be the case the separating conduitwill have its cross-section gradually decreasing from the entrance endof the discharge end thereof.

It is possible to employ a separating conduit of constant cross-sectionand a specially wound magnet providing for advance of the magnetic fieldat a non-uniform velocity, i.e., at a velocity which gradually decreasesfrom the entrance end to the discharge end of the separating conduitconsonant with the natural tendency of the portion of the fluid in theseparating conduit which contains the magnetic material to slow up as itadvances through the separating conduit due to increase in concentrationof magnetic material.

While I prefer for most uses to employ a peripherally closed separatingconduit the separating conduit may in certain applications be open tothe atmosphere.

In any of such cases the'construction is preferably such that theportion of the fluid containing magnetic material is caused to advanceas a stream at a speed which at all points along its course issubstantially equal to the speed of advance of the magnetic field atthose respective points.

- I do not mean to say that the speed of the magnetic particles must beexactly the same as the speed of advance of conduit but the nearer thiscondition is approached the more efficient will be the separatingaction. Separation can be effected though at lower efficiency when thespeed of advance of the magnetic particles is diiferent from the speedof advance of the magnetic field.

Where I refer to substantially magnetic material free liquid I meanliquid from which the bulk of the magnetic material has been removed,not necessarily liquid ap- "proaching complete freedom from magneticmaterial. For example, I would consider liquid containing as little as10 to 15 percent of magnetic material by weight to be substantiallymagnetic material free for certain purposes although generally I wouldexpect that the percentage by weight of magnetic material in mysubstantially magnetic ill-r material free liquid would be substantiallyless than percent, ordinarily of the order of 1 percent or less.

The loss of magnetite and water is very small. By use of there-circulating system shown in Fig. l the buoyancy of the liquid in thereservoir 2 is maintained substantially constant at the desired point asthe quantity of water returned to the reservoir is substantially thesame as the quantity of water withdrawn and the quantity of magnetitereturned is substantially the same as the quantity of the magnetitewithdrawn.

1 thus accomplish in a very simple and efficient way a process whichheretofore has been complicated by the flocculation and consequentnecessity of deflocculation of the magnetic material. Advantages alsoaccrue by reason of the pumping of the liquid through the separatingconduit at a speed such that the contents of the conduit or the portionthereof containing the magnetite moves along the conduit at a speedsubstantially equal to the speed of movement in the same direction ofthe magnetic field. The character of the alternating current magneticfield and the agitation of the particles of magnetite as they advancethrough the separating conduit cooperate to prevent any appreciablepermanent magnetization of the particles of magnetite and hence toprevent flocculation of the magnetite.

While I have shown and described certain present preferred embodimentsof the invention and certain present preferred methods of practicing thesame it is to be distinctly understood that the invention is not limitedthereto but may be otherwise variously embodied and practiced within thescope of the following claims.

I claim:

1. A method of recovering substantially magnetic material free liquidfrom liquid containing magnetic material comprising flowing in a streamliquid containing magnetic material, impelling toward one side of thestream magnetic material in the liquid by a magnetic field, confiningthe dimension of the stream parallel to the direction of magneticimpulsion to a minimum in the zone of entry of the stream into themagnetic field, increasing said dimension in a zone advanced in thedirection of flow relatively to said first mentioned zone, deliveringthe magnetic material at said side of the stream and deliveringsubstantially magnetic material free liquid at the opposite side of thestream.

2. A method of recovering substantially magnetic material free liquidfrom liquid containing magnetic material comprising flowing in a streamliquid containing magnetic material, drawing toward one side of thestream magnetic material in the liquid by a magnetic field, advancing inthe direction of flow at approximately equal speeds the magnetic fieldand that portion of the stream containing the magnetic material,confining the dimension of the stream parallel to the direction ofmagnetic attraction to a minimum in the zone of entry of the stream intothe magnetic field, increasing said dimension in a zone advanced in thedirection of flow relatively to said first mentioned zone, deliveringthe magnetic material at said side of the stream and deliveringsubstantially magnetic material free liquid at the opposite side of thestream.

3. A method of recovering substantially magnetic material free liquidfrom liquid containing magnetic material comprising flowing in a streamliquid containing magnetic material, irnpelling toward one side of thestream magnetic material in the liquid by a magnetic field, confiningthe dimension of the stream parallel to the direction of magneticimpulsion to a minimum in the zone of entry of the stream into themagnetic field, increasing said dimension in a zone advanced in thedirection of flow relatively to said first mentioned zone, decreasing inthe direction of flow the dimension of the stream normal to said firstmentioned dimension, delivering the magnetic material at said side ofthe stream and delivering sub.- stantially magnetic material free liquidat the opposite side of the stream.

4. A method of recovering substantially magnetic material free liquidfrom liquid containing magnetic material comprising flowing in agenerally horizontal stream liquid containing magnetic material, drawingdownwardly magnetic material in the liquid by a magnetic field, movingthe magnetic field in the direction of flow of the liquid, confining thedepth of the stream toa minimum in the zone of entry of the stream intothe magnetic field, increasing the depth of the stream in a zoneadvanced in the direction of flow relatively to said first mentionedzone and delivering substantially magnetic material free liquid fromabove the downwardly drawn magnetic material.

5. Apparatus for recovering substantially magnetic material free liquidfrom liquid containing magnetic material comprising means for flowing ina stream liquid containing magnetic material, means creating a magneticfield moving along the stream in the direction of flow drawing towardone side of the stream magnetic material in the liquid, stream definingmeans confining the dimension of the stream parallel to the direction ofmagnetic attraction to a minimum in the zone of entry of the stream intothe magnetic field and increasing said dimension in a zone advanced inthe direction of flow relatively to said first mentioned zone so thatthe magnetic field and that portion of the stream containing themagnetic material advance in the direction of flow at approximatelyequal speeds, means for delivering the magnetic material at said side ofthe stream and means for delivering substantially magnetic material freeliquid at the opposite side of the stream.

6. Apparatus for recovering substantially magnetic material free liquidfrom liquid containing magnetic material comprising means for flowing ina stream liquid containing magnetic material, means creating a magneticfield drawing toward one side of the stream magnetic material in theliquid, stream defining means confining the dimension of the streamparallel to the direction of magnetic attraction to a minimum in thezone of entry of the stream into the magnetic field andv increasing saiddimension in a zone advanced in the direction of flow relatively to saidfirst mentioned zone while decreasing in the direction of flow thedimension of the stream normal to said first mentioned dimension, meansfor delivering the magnetic material at said side of the stream andmeans for delivering substantially magnetic material free liquid at theopposite side of the stream.

7. Apparatus for recovering substantially magnetic material free liquidfrom liquid containing magnetic material comprising means for flowing ina generally horizontal stream liquid containing magnetic material, meansReferences Cited in the file of this patent UNITED STATES PATENTSGermany Dec. 17, 1942 I

